Nonpolar filaments that are generally found only in multicellular organisms. These intermediate sized (10 nm in diameter) filaments are thinker than their microfilament analog
s, but thinner than microtubule
s, thus the name "intermediate". Intermediate filaments are structural in function, and pass through cell junction
s and intermembrane proteins to pass through several cells and integrate them into tissue (sort of like a wire mesh that provides larger structure and support).
The strength of intermediate filaments is illustrated by claws and hair, which are made up of dead cell
s that are composed mainly of intermediate filaments. This stability extends to the chemical
realm as well. Intermediate filaments are not dynamic
in the way the microtubule
s and microfilament
s are. Instead of constantly stacking and unstacking, it is formed by the relatively stable polymerization into a rope-like structure.
Although IFs are not as dynamic as other filaments,and there are no motor protein
s that are known to work with them, they are even more unusual in that they are composed of 6 (plus or minus depending on how you clasify) different types of subunits. The first two types (acidic
and basic keratins
) combine with each other in various ways (though always 1 acidic to 1 basic) to form the various types necessary for epithelial cell
s (from that in hair, to that in the lumen
The third type do not have to form with any other type (they can form "homopolymeric
" IFs), but they can. This type is found in muscle
cells, as well as neuron
s. The type three Desmin
is particularly important in stabilizing the z disk
The fourth type is found only in the nervous system and are responsible for axon
The fifth type is found only in lens fiber cells.
The final type is found only in the nucleus
(of all eukaryote
s) and make up what is commonly known as the "nuclear lamin
" which is a network that supports the nuclear membrane
(the role of intermediate filament associated protein (IFAP) receptor for lamin B in binding lamin B to the membranes particularly interesting).
s affecting the expression of intermediate filaments can lead to horrible genetic skin blister
ing diseases like epidermolysis bullosa simplex